Vane pump

ABSTRACT

A vane pump includes: a rotor; vanes; a cam ring; pump chambers; a suction port; a discharge port; back-pressure chambers; a discharge-side back pressure port configured to guide working fluid that is discharged from the discharge port to the back-pressure chambers; and suction-side back pressure ports configured to guide the working fluid to the back-pressure chambers. The suction-side back pressure ports are formed to be divided into a low-pressure port and a high-pressure port, the low-pressure port being configured to guide the working fluid in the suction port to the back-pressure chambers, and the high-pressure port being configured to guide the working fluid that is discharged from the discharge port to the back-pressure chambers. The high-pressure port is arranged at the forward-side of the low-pressure port in rotating direction of the rotor.

TECHNICAL FIELD

The present invention relates to a vane pump that is used as a fluidpressure source in a fluid hydraulic apparatus.

BACKGROUND ART

A vane pump includes a rotor in which vanes are received, a cam ringthat has an inner circumferential cam face with which tip portions ofthe vanes slidingly contact, and a side plate that slidingly contactwith one end side of the rotor in the axial direction. The side plate isprovided with a suction port and a discharge port, each of the suctionport and the discharge port is formed in an arc shapes, the suction portguides working fluid into pump chambers defined by the rotor, the camring, and the adjacent vanes, and a discharge port guides the workingfluid discharged from the pump chambers.

Furthermore, the side plate is provided with a back pressure port thatguides the working fluid, which is discharged from the discharge port,to back-pressure chambers defined on the base-end sides of the vanes.With such a configuration, because the vanes are pressed radiallyoutward by the pressure of the working fluid in the back-pressurechambers, tip ends of the vanes can slidingly contact with the innercircumference of the cam ring over the whole circumference of the rotor.

JP2003-97453A discloses a technique where each of a back pressure portat suction side and a back pressure port at discharge side is formed inan arc shape, both ends of the back pressure ports are communicatedthrough orifice grooves, the back pressure port at the suction side isprovided for introducing, to back-pressure chambers, working fluiddischarged from a discharge port in a suction section in which theworking fluid is guided to pump chambers, and the back pressure port atthe discharge side is provided for introducing, to the back-pressurechambers, the working fluid discharged from the discharge port in adischarge section in which the working fluid is discharged from the pumpchambers.

SUMMARY OF INVENTION

However, in the suction section, because the pressure in the pumpchambers is low, the vanes are strongly pressed against the innercircumferential cam face of the cam ring by the pressure in theback-pressure chambers. With this, a sliding resistance between the tipends of the vanes and the inner circumferential cam face is increased toincrease rotating load of the rotor, and thereby, efficiency of the vanepump is deteriorated.

Thus, it is considered to block the communication between the backpressure port at the suction side and the back pressure port at thedischarge side and to introduce the working fluid that flows through thesuction port to the back pressure port at the suction side. With such aconfiguration, because the pressure in the back-pressure chambers in thesuction section becomes low, the sliding resistance between the tip endsof the vanes and the inner circumferential cam face is reduced, andthereby, the deterioration of the efficiency of the vane pump issuppressed.

However, if the pressure in the back pressure port at the suction sideis lowered as described above, because the pressure in the pump chambersand the pressure in the back-pressure chambers become substantially thesame in the suction section, a force acting in the direction in whichthe vanes project in the suction section is solely the centrifugal forcegenerated by the rotation of the rotor. Therefore, because the pressingforce for the vanes is insufficient when the vanes move to the dischargesection, there is a risk that the vanes are separated from the innercircumferential cam face, making the pump chamber in the dischargesection to communicate with the pump chamber in the suction section, andcausing the pump discharge pressure to drop.

The present invention aims to provide a vane pump that is capable ofpreventing separation of vanes when moving to a discharge section whilesuppressing a sliding resistance of the vanes in a suction section.

According to one aspect of the present invention, a vane pump that isused as a fluid pressure source includes: a rotor configured to berotationally driven; a plurality of slits formed in a radiating patternso as to open to an outer circumference of the rotor; vanes slidablyreceived in the respective slits; a cam ring that has an innercircumferential cam face with which tip portions of the vanes slidinglycontact, the tip portions being end portions of the vanes in directionprojecting from the slits; pump chambers defined by the rotor, the camring, and the adjacent vanes; a suction port configured to guide workingfluid that is to be sucked to the pump chambers; a discharge portconfigured to guide the working fluid that is discharged from the pumpchambers; back-pressure chambers formed in the slits, the back-pressurechambers being partitioned by base-end portions of the vanes, thebase-end portions being end portions at the opposite side from the tipportions; a discharge-side back pressure port configured to guide theworking fluid that is discharged from the discharge port to theback-pressure chambers in a discharge section in which the pump chambersare in communication with the discharge port; and suction-side backpressure ports configured to guide the working fluid to theback-pressure chambers in a suction section in which the pump chambersare in communication with the suction port. The suction-side backpressure ports are formed to be divided into a low-pressure port and ahigh-pressure port, the low-pressure port being configured to guide theworking fluid in the suction port to the back-pressure chambers, thehigh-pressure port being configured to guide the working fluid that isdischarged from the discharge port to the back-pressure chambers, andthe high-pressure port is arranged at the forward-side of thelow-pressure port in rotating direction of the rotor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view showing a vane pump according to an embodiment ofthe present invention.

FIG. 2 is a front view of a side plate.

FIG. 3 is a front view of a pump cover.

FIG. 4 is a front view showing a vane pump according to a comparativeexample.

FIG. 5 is a front view of a side plate according to the comparativeexample.

FIG. 6 is a front view of a pump cover according to the comparativeexample.

DESCRIPTION OF EMBODIMENTS

With reference to the drawings, an embodiment of the present inventionwill be described below.

FIG. 1 is a front view of a vane pump 100 according to this embodiment,and is a diagram viewed from a direction along a drive shaft 20 in astate in which a pump cover 80 has been detached. FIG. 2 is a front viewof a side plate 70 and is a diagram viewed from the same direction asthat in FIG. 1. FIG. 3 is a front view of the pump cover 80 and is adiagram showing a state in which the pump cover 80 that has beendetached from the vane pump 100 shown in FIG. 1 is turned over about theaxis along the up and down direction on the plane of figure.

The vane pump 100 is a variable displacement vane pump, and is used as afluid pressure source for a fluid hydraulic apparatus, such as, a powersteering apparatus, a continuously variable transmission, or the like,mounted on a vehicle. Oil, aqueous alternative fluid of other type, orthe like may be used as working fluid. Although a variable displacementvane pump is illustrated in this embodiment, the vane pump may be offixed displacement type.

The vane pump 100 is driven by an engine (not shown) etc., for example,and generates fluid pressure as a rotor 30 that is linked to the driveshaft 20 is rotated clockwise as shown by an arrow in FIG. 1.

The vane pump 100 includes a pump body 10, the drive shaft 20 that isrotatably supported by the pump body 10, the rotor 30 that isrotationally driven by being linked to the drive shaft 20, a pluralityof vanes 40 that are provided so as to be capable of reciprocating inthe radial direction relative to the rotor 30, a cam ring 50 thataccommodates the rotor 30 and the vanes 40, and an annular adapter ring60 that surrounds the cam ring 50.

In the rotor 30, a plurality of slits 31 having openings on the outercircumferential surface of the rotor 30 are formed in a radiatingpattern with predetermined gaps therebetween. The vanes 40 are insertedinto the respective slits 31 in a freely slidable manner. At thebase-end sides of the slits 31, back-pressure chambers 32 are formed bybeing defined by base-end portions 41 of the vanes 40, which are endportions at the opposite side from the direction in which the vanes 40project from the slits 31, and the working fluid is guided to theback-pressure chambers 32. The vanes 40 are pressed in the direction inwhich the vanes 40 project from the slits 31 by the pressure of theback-pressure chambers 32.

In the pump body 10, a pump accommodating concaved portion 11 thataccommodates the adapter ring 60 is formed. The side plate 70 (see FIG.2) is arranged on a bottom surface of the pump accommodating concavedportion 11 so as to abut against the one side in the axial direction(back side in FIG. 1) of each of the rotor 30, the cam ring 50, and theadapter ring 60. An opening of the pump accommodating concaved portion11 is closed with the pump cover 80 (see FIG. 3) that abuts against theother side (front side in FIG. 1) of each of the rotor 30, the cam ring50, and the adapter ring 60. The pump cover 80 and the side plate 70 arearranged in a state in which both side surfaces of each of the rotor 30,the cam ring 50, and the adapter ring 60 are sandwiched. Pump chambers33 are defined between the rotor 30 and the cam ring 50 by beingpartitioned by the respective vanes 40.

As shown in FIG. 2, on the side plate 70, a suction port 71 for guidingthe working fluid into the pump chambers 33 and a discharge port 72 fordischarging the working fluid in the pump chambers 33 and guiding it tothe fluid hydraulic apparatus are formed. The suction port 71 and thedischarge port 72 are individually formed so as to have arc shapescentered at a center O of the drive shaft 20.

As shown in FIG. 3, a suction port 81 and a discharge port 82 are formedon the pump cover 80 at respective positions symmetrical to those on theside plate 70. In other words, the suction port 81 on the pump cover 80is in communication with the suction port 71 on the side plate 70through the pump chambers 33, and the discharge port 82 on the pumpcover 80 is in communication with the discharge port 72 on the sideplate 70 through the pump chambers 33.

Referring back to FIG. 1, the cam ring 50 is an annular member, and hasan inner circumferential cam face 51 with which tip portions 42 of thevanes 40, which are end portions of the vanes 40 in the directionprojecting from the slits 31, slidingly contact. On the innercircumferential cam face 51, a suction section in which the workingfluid is sucked through the suction ports 71 and 81 by the rotation ofthe rotor 30 and a discharge section in which the working fluid isdischarged through the discharge ports 72 and 82.

The suction ports 71 and 81 are formed so as to penetrate the side plate70 and to communicate with a tank (not shown) through a suction passage12 formed on the pump body 10 and the pump cover 80, and the workingfluid in the tank is supplied to the pump chambers 33 from the suctionports 71 and 81 on the side plate 70 and the pump cover 80,respectively, through the suction passage 12.

The discharge port 72 is formed so as to penetrate the side plate 70 andto communicate with a high-pressure chamber (not shown) formed on thepump body 10. The high-pressure chamber is in communication with thefluid hydraulic apparatus (not shown) outside the vane pump 100 througha discharge passage (not shown). In other words, the working fluid thatis discharged from the pump chambers 33 is supplied to the fluidhydraulic apparatus through the discharge ports 72 and 82, thehigh-pressure chamber, and the discharge passage.

The adapter ring 60 is accommodated in the pump accommodating concavedportion 11 of the pump body 10. A support pin 61 is interposed betweenthe adapter ring 60 and the cam ring 50. The cam ring 50 is supported bythe support pin 61 such that the cam ring 50 swings about the supportpin 61 inside the adapter ring 60, and thereby, is made eccentric to thecenter O of the drive shaft 20.

A seal member 63 is interposed in a groove 62 of the adapter ring 60,and the seal member 63 slidingly contacts with the outer circumferentialsurface of the cam ring 50 during the swing of the cam ring 50. A firstfluid pressure chamber 64 and a second fluid pressure chamber 65 arepartitioned by the support pin 61 and the seal member 63 in a spacebetween the outer circumferential surface of the cam ring 50 and theinner circumferential surface of the adapter ring 60.

The cam ring 50 swings about the support pin 61 by a pressure differencebetween the first fluid pressure chamber 64 and the second fluidpressure chamber 65. As the cam ring 50 swings, the amount ofeccentricity of the cam ring 50 with respect to the rotor 30 is changed,and the discharge capacity of the pump chambers 33 is changed. When thecam ring 50 swings counterclockwise about the support pin 61 in FIG. 1,the amount of eccentricity of the cam ring 50 with respect to the rotor30 is reduced, and thus, the discharge capacity of the pump chambers 33is reduced. In contrast, as shown in FIG. 1, when the cam ring 50 swingsclockwise about the support pin 61, the amount of eccentricity of thecam ring 50 with respect to the rotor 30 is increased, and thus, thedischarge capacity of the pump chambers 33 is increased.

A restricting portion 66 that restricts movement of the cam ring 50 inthe direction in which the amount of eccentricity with respect to therotor 30 is reduced and a restricting portion 67 that restricts movementof the cam ring 50 in the direction in which the amount of eccentricitywith respect to the rotor 30 is increased are respectively formed on theinner circumferential surface of the adapter ring 60 in a swelledmanner. In other words, the restricting portion 66 defines the minimumamount of eccentricity of the cam ring 50 with respect to the rotor 30,and the restricting portion 67 defines the maximum amount ofeccentricity of the cam ring 50 with respect to the rotor 30.

The pressure difference between the first fluid pressure chamber 64 andthe second fluid pressure chamber 65 is controlled by a control valve(not shown). The control valve controls the working fluid pressure inthe first fluid pressure chamber 64 and the second fluid pressurechamber 65 such that the amount of eccentricity of the cam ring 50 withrespect to the rotor 30 is reduced with the increase in the rotationspeed of the rotor 30.

Back pressure ports for guiding the working fluid to the back-pressurechambers 32 will be described below.

As shown in FIG. 2, a discharge-side back pressure port 73 that is incommunication with the back-pressure chambers 32 in the dischargesection and suction-side back pressure ports 74 that are incommunication with the back-pressure chambers 32 in the suction sectionare formed on the side plate 70.

The discharge-side back pressure port 73 is formed so as to have an arcshape centered at the center O of the drive shaft 20 over the wholeregion of the discharge section. The suction-side back pressure ports 74include a low-pressure port 75 that is provided at the rearward-side inthe rotating direction of the rotor 30 in the suction section, and ahigh-pressure port 76 that is provided at the forward-side in therotating direction of the rotor 30 in the suction section. In otherwords, the back-pressure chambers 32 are made to communicate with thedischarge-side back pressure port 73, the low-pressure port 75, and thehigh-pressure port 76 in this order by the rotation of the rotor 30.

The low-pressure port 75 and the high-pressure port 76 are provided in aseparated manner so as not to communicate with each other. On the otherhand, the discharge-side back pressure port 73 and the high-pressureport 76 are in communication through a narrow groove 77 having thecross-sectional area smaller than that of the high-pressure port 76.Furthermore, the high-pressure port 76 is in communication with thehigh-pressure chamber through a through hole 78 penetrating the sideplate 70.

As shown in FIG. 3, a discharge-side back pressure port 83, alow-pressure port 85, and a high-pressure port 86 are formed on the pumpcover 80 at respective positions symmetrical to those on the side plate70. The discharge-side back pressure port 83 and the high-pressure port86 are in communication through a narrow groove 87 as with the sideplate 70. Furthermore, the low-pressure port 85 is in communication withthe suction passage 12 through a through hole 88.

In the above-described configuration, the pressure of the working fluidthat is discharged from the pump chambers 33 is guided to the dischargeports 72 and 82, the high-pressure chamber, the through hole 78, and thehigh-pressure ports 76 and 86, and then, guided to the discharge-sideback pressure ports 73 and 83 through the narrow grooves 77 and 87. Thepressure of the working fluid in the high-pressure ports 76 and 86 andthe discharge-side back pressure ports 73 and 83 is guided to theback-pressure chambers 32 just before the suction section ends and inthe discharge section, and the pressure of the working fluid in theback-pressure chambers 32 presses the vanes 40 in the direction in whichthe vanes 40 project towards the cam ring 50 from the rotor 30.

On the other hand, the working fluid in the suction passage 12 is guidedto the low-pressure ports 75 and 85 through the through hole 88 that isprovided in the low-pressure port 85 of the pump cover 80. The workingfluid in the low-pressure ports 75 and 85 is guided to the back-pressurechambers 32 in the suction section.

When the vane pump 100 is operated, the vanes 40 are biased in thedirection in which the vanes 40 project from the slits 31 by a biasingforce by the pressure of the working fluid in the back-pressure chambers32 that presses the base-end portions 41 of the vanes 40 and by thecentrifugal force that is caused by the rotation of the rotor 30, andthereby, the tip portions 42 of the vanes 40 slidingly contact with theinner circumferential cam face 51 of the cam ring 50.

In the suction section, the vanes 40 that slidingly contact with theinner circumferential cam face 51 are projected from the rotor 30,thereby causing the pump chambers 33 to expand, and the working fluid issucked into the pump chambers 33 from the suction ports 71 and 81. Inthe discharge section, the vanes 40 that slidingly contact with theinner circumferential cam face 51 are pushed back into the rotor 30,thereby causing the pump chambers 33 to contract, and the working fluidthat is pressurized in the pump chambers 33 is discharged from thedischarge ports 72 and 82.

A vane pump 200 according to a comparative example will be describedbelow.

FIG. 4 is a front view of the vane pump 200 according to the comparativeexample, and is a diagram viewed from the direction along the driveshaft 20 in a state in which a pump cover 180 has been removed. FIG. 5is a front view of a side plate 170 according to the comparativeexample. FIG. 6 is a front view of the pump cover 180 according to thecomparative example.

With the vane pump 200 according to the comparative example,suction-side back pressure ports 174 and 184 are not divided into alow-pressure port and a high-pressure port. In other words, thesuction-side back pressure ports 174 and 184 are formed so as to havearc shapes centered at the center O of the drive shaft 20 over the wholeregion of the suction section.

Furthermore, the suction-side back pressure ports 174 and 184 anddischarge-side back pressure ports 173 and 183 are in communicationthrough narrow grooves 177 and 187. The suction-side back pressure port174 is in communication with the high-pressure chamber through somethrough holes 178 provided at both ends of the suction-side backpressure port 174 so as to penetrate the side plate 170.

With such a configuration, the pressure of the working fluid that isdischarged from the pump chambers 33 is introduced to discharge ports172 and 182, the high-pressure chamber, the through holes 178, thesuction-side back pressure ports 174 and 184, and then, introduced tothe discharge-side back pressure ports 173 and 183 through the narrowgrooves 177 and 187. Therefore, the suction-side back pressure ports 174and 184 and the discharge-side back pressure ports 173 and 183 are bothfilled with the high-pressure working fluid that is discharged from thepump chambers 33.

In the suction section, because the pressure in the pump chambers 33 islow, the vanes 40 are strongly pressed against the inner circumferentialcam face 51 of the cam ring 50 due to the pressure of the high-pressureworking fluid in the back-pressure chambers 32. With this, there is arisk that the efficiency of the vane pump 200 is deteriorated due to theincrease in the sliding resistance between the tip portions 42 of thevanes and the inner circumferential cam face 51, which in turn increasesthe rotating load of the rotor 30.

In addition, it is considered to suppress the above-described slidingresistance by blocking the communication between the suction-side backpressure ports 174 and 184 and the discharge-side back pressure ports173 and 183, and by introducing the working fluid in a suction passageinto the suction-side back pressure ports 174 and 184.

However, if the pressure in the suction-side back pressure ports 174 and184 is decreased as described above, because the pressure in the pumpchambers 33 and the pressure in the back-pressure chambers 32 becomesubstantially the same in the suction section, a force acting in thedirection in which the vanes 40 project in the suction section is solelythe centrifugal force generated by the rotation of the rotor 30.Therefore, the pressing force for the vanes 40 is insufficient when thevanes 40 move to the discharge section, and there is a risk that thepump chamber 33 in the discharge section and the pump chamber 33 in thesuction section are made to communicate through a gap formed between thevane 40 and the inner circumferential cam face 51, causing the dischargepressure of the vane pump 200 to drop.

Thus, as shown in FIGS. 2 and 3, this embodiment is configured such thatthe suction-side back pressure ports 74 are divided into thelow-pressure port 75 and the high-pressure port 76, the high-pressureworking fluid in the high-pressure chamber is guided to thehigh-pressure port 76, and the low-pressure working fluid in the suctionpassage 12 is guided to the low-pressure port 75.

With such a configuration, along the rotating direction of the rotor 30in the first half region of the suction section, the back-pressurechambers 32 are made to communicate with the low-pressure port 75,causing the pressing force for the vanes 40 to drop. Therefore, becausethe sliding resistance between the vanes 40 and the cam ring 50 isreduced, the efficiency of the vane pump 100 is increased.

In addition, in the region just before ending the suction section,because the back-pressure chambers 32 are made to communicate with thehigh-pressure port 76, the high-pressure working fluid is introducedfrom the high-pressure chamber to the back-pressure chambers 32, and thevanes 40 can reliably be pressed against the inner circumferential camface 51 before moving into the discharge section. Therefore, theboundary between the suction section and the discharge section canreliably be defined with the vanes 40, and drop in the dischargepressure of the vane pump 100 can reliably be suppressed.

According to the embodiment mentioned above, the advantages describedbelow are afforded.

The suction-side back pressure ports 74 are formed so as to be dividedinto the low-pressure port 75 and the high-pressure port 76, and thehigh-pressure port 76 is arranged at the forward-side of thelow-pressure port 75 in the rotating direction of the rotor 30. Inaddition, the working fluid in the suction passage 12 is guided to thelow-pressure port 75, and the high-pressure working fluid in thehigh-pressure chamber is guided to the high-pressure port 76.

With such a configuration, while the back-pressure chambers 32 are incommunication with the low-pressure port 75 in the suction section,because the pressure in the back-pressure chambers 32 becomes low toreduce the pressing force for the vanes 40, the sliding resistancebetween the vanes 40 and the inner circumferential cam face 51 issuppressed, and the efficiency of the vane pump 100 can be improved.

In addition, because protruding level of the vanes 40 reduces in thesuction section, it is possible to suppress interference to a flowchannel of the working fluid that is to be sucked into the pump chambers33 from the suction ports 71 and 81 when the vanes 40 pass through thesuction section. Thus, a sucking efficiency of the working fluid can beimproved.

Furthermore, when the back-pressure chambers 32 are made to communicatewith the high-pressure port 76 in the suction section, because thepressure in the back-pressure chambers 32 becomes high to increase thepressing force for the vanes 40, the vanes can be caused to slidinglycontact reliably with the inner circumferential cam face 51 beforemoving into the discharge section. Thus, the boundary between thesuction section and the discharge section can reliably be defined withthe vanes 40 that slidingly contact with the inner circumferential camface 51, and the drop of the discharge pressure of the vane pump 100 canbe prevented.

In particular, even when the pump is started at low temperature at whichthe working fluid is more viscous, because the vanes 40 that are settledin the slits 31 can be made projected quickly to slidingly contact withthe inner circumferential cam face 51, the discharge pressure of thevane pump 100 is increased promptly, and a startability of the vane pump100 can be improved.

Furthermore, because the discharge-side back pressure port 73 is made tocommunicate with the high-pressure port 76 through the narrow groove 77having the cross-sectional area smaller than that of the high-pressureport 76, the tip portions 42 of the vanes 40 are pushed by the innercircumferential cam face 51 such that the vanes 40 are pushed into theslits 31 in the discharge section, and the resulting volume reduction ofthe back-pressure chambers 32 causes the working fluid flowing into thedischarge-side back pressure port 73 to communicate with thehigh-pressure port 76 as a narrowed flow through the narrow groove 77.Therefore, because the pressure in the discharge-side back pressure port73 is held at higher level than that in the high-pressure port 76 by theamount of the pressure loss at the narrow groove 77, the force forprojecting the vanes 40 can be maintained at the high level in thedischarge section, and the slidingly contacted state between the vanes40 and the inner circumferential cam face 51 can reliably be maintained.

Embodiments of this invention were described above, but the aboveembodiments are merely examples of applications of this invention, andthe technical scope of this invention is not limited to the specificconstitutions of the above embodiments.

For example, in the above-mentioned embodiment, although thedischarge-side back pressure port 73 and the suction-side back pressureports 74 are individually provided on the side plate 70 and the pumpcover 80, the discharge-side back pressure port 73 and the suction-sideback pressure ports 74 may be provided on only one of the side plate 70and the pump cover 80. In a case in which the discharge-side backpressure port 73 and the suction-side back pressure ports 74 areprovided on the side plate 70 only, a new through hole may be providedsuch that the low-pressure port 75 of the side plate 70 is made tocommunicate with the suction passage 12. In a case in which thedischarge-side back pressure port 73 and the suction-side back pressureports 74 are provided on the pump cover 80 only, a new through hole maybe provided such that the high-pressure port 86 of the pump cover 80 ismade to communicate with the high-pressure chamber.

This application claims priority based on Japanese Patent ApplicationNo. 2013-044575 filed with the Japan Patent Office on Mar. 6, 2013, theentire contents of which are incorporated into this specification.

1. A vane pump that is used as a fluid pressure source, comprising: arotor configured to be rotationally driven; a plurality of slits formedin a radiating pattern so as to open to an outer circumference of therotor; vanes slidably received in the respective slits; a cam ring thathas an inner circumferential cam face with which tip portions of thevanes slidingly contact, the tip portions being end portions of thevanes in direction projecting from the slits; pump chambers defined bythe rotor, the cam ring, and the adjacent vanes; a suction portconfigured to guide working fluid that is to be sucked to the pumpchambers; a discharge port configured to guide the working fluid that isdischarged from the pump chambers; back-pressure chambers formed in theslits, the back-pressure chambers being partitioned by base-end portionsof the vanes, the base-end portions being end portions at the oppositeside from the tip portions; a discharge-side back pressure portconfigured to guide the working fluid that is discharged from thedischarge port to the back-pressure chambers in a discharge section inwhich the pump chambers are in communication with the discharge port;and suction-side back pressure ports configured to guide the workingfluid to the back-pressure chambers in a suction section in which thepump chambers are in communication with the suction port; wherein thesuction-side back pressure ports are formed to be divided into alow-pressure port and a high-pressure port, the low-pressure port beingconfigured to guide the working fluid in the suction port to theback-pressure chambers, and the high-pressure port being configured toguide the working fluid that is discharged from the discharge port tothe back-pressure chambers, and the high-pressure port is arranged atthe forward-side of the low-pressure port in rotating direction of therotor.
 2. The vane pump according to claim 1, wherein the high-pressureport is in communication with the discharge-side back pressure portthrough a narrow groove having smaller cross-sectional area than that ofthe high-pressure port.
 3. The vane pump according to claim 1, furthercomprising: a side plate provided on one end side in an axial directionof the rotor, the side plate abutting against the rotor and the camring; and a pump cover provided on other end side in the axial directionof the rotor, the pump cover abutting against the rotor and the camring; wherein the discharge-side back pressure port and the suction-sideback pressure ports are provided on at least one of the side plate andthe pump cover.